Vacuum rectifying column



Oct. 17, 1939. I 3, HICKMAN 2,176,498

' VACUUM RECTIFYING 'COLUMN Filed July 2, 19 37 WM 45 H 57 56 47 W1 46ll KenneihCDHicKman INVENTOR ATTORNEYS Patented Oct. 17, 1939 UNITEDSTATES PATENT OFFlCE VACUUM RECTIFYING COLUMN of Delaware ApplicationJuly 2, 1937, Serial No. 151,715 In Great Britain July 6, 1936 L 9Claims.

This invention relates to improvements in the fractionation orrectification of vapors under vacuum and more particularly toimprovements in vacuum rectifying columns.

The conventional rectifying columnfor use at ordinary pressures isfilled with a series of bubble cap plates which ensures thorough washingof the reflux by the ascending vapors. This construction is known to be'unsatisfactory for vaclo uum and particularly high vacuum fractionation,due to the high resistance to the flow of vapors through the column.Relatively high pressures therefore prevail in the still and column,even though high capacity evacuating pumps are em- 18 ployed. To avoidthese disadvantages, it has ,be-

oome common practice to employ plates which are so designed and locatedthat the ascending vapors are substantially unconstricted in passingthrough the column. This construction avoids w pressure drop to aconsiderable extent, but does not avoid other dimculties. The vaporvelocity under vacuum conditions is so high that in a column of thistype condensate is swept along with the vapor stream and is, therefore,substantially prevented from freely flowing countercurrent thereto, asis necesary to obtain efiective interchange between the two. Poorfractionation and flooding of the column, therefore, takes place. Thisis especially troublesome at low presan sures, such as at .001 to 50 mm.where vapor velocities are extremely high.

This invention has for its object to overcome the above deficiencies ofvacuum, and particularly high vacuum, rectification. Another object isto provide an improved method of vacuum rectification. A further objectis to provide methed and means whereby the adverse effect of the highvelocity vapor streams is substantially avoided. A still further objectis to provide an proved vacuum rectifying column. Other objects willbecome apparent from the following detailed description.

These and other objects are accomplished by the herein describedinvention, which in general Q comprises collecting the condensate froman upper plate and passing it to the next lower plate in the columnwhile protecting it from the action of the vapor stream.

To facilitate the description of my invention,

no reference is made to the accompanying drawing in which:

Fig. 1 is a vertical section in perspective'of one type of fractionatingcolumn embodying the principles of my invention:

If Fig. 2 is a vertical section of a modification of the column shown inFig. 1, being provided with semi-circular plates;

Fig. 3 is a horizontal section taken on line 3-3 of Fig. 2; I

Fig. 4 is a vertical section in perspective of 241- 6 paratussubstantially the same as that illustrated in Fig. 2, but being providedwith external heating elements and means for aiding in the evendistribution of condensate over the surface of the plates. 10

Referring to Fig. 1, reference numeral 2 deslgr nates a cylindricalcolumn which is connected at the base to a source of vapor and. which isprovided at the top with a jacket 3 through which cooling fluid iscirculated in order to cool the upper walls of the main casing 2.Numerals t, 5, t and l designatecircular plates supported by and fixedto the walls of the cylindrical casing 2 in such a manner that they areapproximately horizontal. These plates are provided with a cenat tralopening, the inside edge of which is turned under to form gutters 3, 9,it and M, respectively. Numerals i2, 53, it and i5 designate circularplates which approximately correspond in diameter to the diameter of thecentral opening in plates li. The outside edges of plates i2--iii areturned under to form gutters 2d, at, 22 and 23. Plate I2 is rigidlysupported in the central position, illustrated by a series of pipes 25,which communicate with gutter 8 and are rigidly fixed 5p thereto andwhich are also rigidly fixed to the upper surface of plate it. Thesepipes are provided with openings 25 at a position just above the surfaceof plate It, located upon the side of the pipe facing towards the centerof the col- @5 umn. Plate is is similarly supported by a series of pipes26 located about its periphery, which communicate with the gutter 9 andare provided with openings 2? at the base thereof. Another series ,ofconduits it, having openings ii in the g base thereof, connect to gutter2i and deliver liquid therein onto the upper surface of plate 3. Plateit is supported by a similar series of conduits it, which communicatewith gutter ill and deliver liquid through openings it onto the up- (itper surface of plate it, and another set of lower conduits 28, whichdeliver liquid from gutter 22 onto the upper surface of plate 5 throughopenings 29. Plate i5 is supported in substantially the same way byconduits 30 communicating with gutter H and having openings 3! in thebase thereof, and by a similar series of lower conduits 32 provided withopenings 33 which concated openings 34-31, over each of which issuspended a cap 38. The .outside peripheries of plates 4'l are notchedat 46 to provide openings for the flow of condensate from the upperside, down onto the lower side of the plate. Numeral 45 designates anannular gutter which is connected to a withdrawal conduit 41.

Referring to Figs. 2 and 3, numeral 55 designates the casing of afractionating or. rectifying column which is provided with a dome 56 andwhich is connected to conduit 57 at its upper end. Numerals 5B, 59, 66and Bi designate approximately horizontal semi-circular. plates rigidlyfixed to the wals of the main casing 55 and which are provided with aseries of openings 62 about the periphery which are in close proximitytothe wall of casing 55. Numerals 53, 64, 65 and 66 designate guttersformed at the free edge of the semi-circular plates 58-6l by turning theg edge thereof in the manner illustrated. A plurality of conduits 6'!communicate with gutter 66 and terminate a short distance above thesurface of plates 66. A similar series of conduits 66 communicatewith'gutter 65 and terminate a short 3; distance above the surface ofplate 69. Another similar set of conduits 69 communicate with gut-. ter64 and terminate a short distance above the surface of plate 58.

Referring to Fig. 4, numerals 15, 16, Hand 18 a designate a serratedblade which acts as a weir in evenly distributing liquid over thesurface of plates 58, 59, 66 and 6f. Numerals l9 and 86' designateexternal heating units, preferably electrical heating pads, which arelocated on diametrically opposite sides of the column 2 and in positionscorresponding to the location of the ends of the gutters 63, 64, 65 and66.

In operating the apparatus of Fig. 1, cooling fluid is circulated in thespace between the upper walls of column 2 and jacket 3. The upper end 5course, must be gas tight.

of the column 2 is connected to vacuum pumps having suficient capacityto evacuate the system 'to the desired low pressure. The base of thecolumn is connected to the vapor source which, of The vapors ascendthrough the column passing into the space between plate l2 and plate 4.In passing through this space, the vapors necessarily must flow towardthe axis of the column. The vapors then are reversed in their path offlow and pass between the plate 4 and central plate l3, the vaporspassing toward the outside walls of the casing 2. This repeated reversalof the direction of fiow of the vapors takesplace until they eventuallypass 5 through the central opening in the top plate I and are condensedupon the cold upper walls of column 2. Condensate flows into gutter and.is withdrawn through conduit 41.

Less volatile constituents condense upon the co various plates as thevapors pass in the zigzag path through the column. Condensate from plate1 'flows to the openings 46 about the periphery thereof, down and ontothe under surface of the plate. The vapors ascending the-col- 45 mu atthis point are flushing or brushing the under surface of plate I in adirection towards the .axis of the column. Therefore, liquid passingvthrough the openings 46 is caused to fiow into the gutter H by thisaction of the vapors.

.70 At the same time, interchange between the film of condensate and thevapors take place and volatile components thereof are again vaporizedand carried along with the vapor stream;*"The washed liquid collectingin gutter H flows down through conduits 30 onto the upper surface ,ofplate l5.

The vapors in contact with the upper surface of this plate are alsopassing in a direction toward .the axis of the column and the liquidflowing from these conduits is, therefore, blown towards the opening 31and passes therethrough onto the under surface of plate IS. Theascending vapors in contact with the under surface of plate l5 arepassing at high velocity towards the ofiter walls of the column and theliquid passing through the onto the upper surface of plate 6, isblownover to'the wall of casing 2, passes through the openings 46 ontothe under surface of plate 6 and is then blown into gutter I6.Substantially the same action takes place on each of the sets of platesdown through the column. 4

It is apparent that, by the construction illustrated, the high velocityvapors are caused to pass into intimate contact with a large area ofcondensate and that effective interchange takes place in its passagethrough the column. It is also apparent that washing of the condensatein an upward direction is avoided by passing it in protected paths in adownward direction at intervals while intermittently exposing it to thewashing action of the vapor. The high velocity vapors are also caused tohelp force the liquids in the downward direction instead of forcing themin an upward direction as isusual with conventional vacuum columnconstruction.

In operating the apparatus of Fig. 3, conduit end of the column isconnected to a source of vapor such as the pot of a still. The ascendingvapors pass into contact with the bottom surface of plate 58 and areforced to pass to the diametrically opposite side of the column, asillustrated by the long arrows. The vapors then pass along the bottomsurface of plate 59 and are forced to pass to the opposite side of thecolumn. In this way, the vapors take a zigzag course up through thecolumn and eventually pass into the conduit 51 and thence into thecondenser. collecting upon the top surface of plate 6| flows through theopening 62, along the bottom of the plate 6|, where the force of thevapors blows it as a thin film into gutter 66. The direction of flow ofcondensate is shown by the short arrows.

The liquid then fiows through conduits 6'! onto plate 66 where theaction of the -vapors causes it to flow as a film into gutter 65.Substantially the same action takes place on plates 59 and 58. Thecondensate is, therefore, caused to flow both by gravity arid by thedynamic action of the vapors in a downward direction through the columnwhile effective interchange between large areas of the condensate andlarge volumes of the vapors takes place. Due to the wide spacing betweenthe plates of all of the figures. slight resistanceto the flow of vaporsis offered.

The operation of the apparatus of Fig. 4 is substantially the same asthat of Fig. 2 except that heating elements 19 and cause vaporization ofcondensate collecting upon the walls of the column in their immediatevicinity. Such vapor- Condensate nation is advantageous, since the highvelocity 1| ing from the spirit or scope of my invention. For

instance, the entire outs'ide surface of the column a vance 'and passedwith the main vapor stream into interchange with the condensate. Theelements 15, l6, l1 and I8 cause even distribution of condensate overthe entire surface of the plates 58 to 6|.

Many changes and variations canv be made in the above describedapparatus, without departmay be jacketed to provide for the circulationof a cooling or heating fluid. Also, certain sections of the-column maybe jacketed to enable the control of the temperature of any particularzone or area in the column. It is also desirable in many cases toprovide part or all of the column with an insulating jacket or laggingto prevent heat losses and thusavold the necessity of adding orsubtracting heat. The column will be heated by vapors to an extentdepending upon the rate of distillation whch is, in turn, controlled bythe temperature of the still. Heating of the column will not usually benecessary except with very low vapor pressure compounds or with very lowrates of distillation. The number of plates employed depends upon thedegree of separation required and the rate of distillation and can be.

varied within wide limits to suit these requirements. The plates mayslant slightly upwards or' downwards, but approximately horizontalplates are preferred, since they increase the rate of downward flowcaused by the action of the vapors. If it is desired to fractionateunder molecular distillation conditions, the plates can be spaced in thetower at distances of less than the mean free path under the particularpressures employed.

it will be apparent that the base of the column can be connected to anywell known type of vaporizing apparatus, such as an ordinary pot still.Also, the base of the column may be used as the vapor source in wellknown manner, by disposing a heating element therein and introducing thematerial to be vaporized in ordinary or preheated condition. Sincematerials which are usually distilled under vacuum conditions have lowvapor pressures and are difficultly volatile, it is best to employ aflash vaporizer as a vapor source. These permit almost instantaneousvaporization of small amounts of the material and avoid considerabledecomposition due to the fact that all of the material is not heatedduring the whole distillation period. A flash vaporizer in which smallamounts of the material are caused to flow over a heated revolvingsurface by centrifugal force is particularly advantageous.

Since the velocities of vapors at pressures of below mm. such as at .001to 50 mm. are exceptionally high, little interchange between vapor andcondensate takes place in towers of the prior art. My invention is,therefore, of particular value for fractionations carried out withinthis pressurerange. It is especially intended for use with vaporsentering the bottom of the column at pressures of .01 to 50 mm. andparticularly .1 to 10 mm., and leaving at the top at pressures of .001to 20 mm.

Due to the fact that the edges of the plates are turned under to collectany condensate on the plate, all-splashing and dropping is substantiallyavoided and this fact materially contributes to the avoidance ofintrainment. Since the features of my invention permit the use of widelyspaced plates which have been found to be necessary in vacuum, andparticularly in high vacuum dlstillations, substantially all backpressure problems due to constriction of vapors are avoided. Theoutstanding advantage of the construction described is that obstructionto reverse passage is avoided, since the vapors are prevented fromcoming in contact with condensate at the time that it is flowing towardsthe base of the column. However, the vapors are contacted at intervalswith the condensate while it is in the form of films of large surfacearea. During such contact the condensate travelsiin the same directionas the vapors and yet it is always being carried counter-current to thevapors by the gutters and conduits. However, even though the vapors andcondensate travel in the same direction during contact, undesirableentrainment does not take place and the condensate is in fact helped toflow in a counter-current direction. At the same time very effectiveinterchange takes place between the two.

What I claim is: I

1. A vacuum fractionating column of the character described andcomprising in combination, a plurality of approximately superimposedplates, which are'widely spaced with respect to each other, which have aconsiderably smaller area than the cross sectional area of the columnand which are adapted to retain condensate in the form of a film andmeans for conveying condensate from each of the plates to the nextlowest to the surface of the next lowest plate while protecting it fromthe action of the high velocity vapor stream.

3. A vacuum fractionating column comprising in combination, a maincolumn casing, a plurality of approximately horizontal superimposedplates which permit substantially unconstricted flow of vapor throughthe column which plates are so constructed that condensate is caused toflow thereover in the form of a thin film by contact with the movingvapor, and means located upon the plates for collecting condensate andpassing it to the surface of the next lowest plate while protecting itfrom the high velocity vapor stream.

4. A vacuum fractionating column comprising in combination, a tower ormain column casing, a;

5. A vacuum fractionating column comprising in combination, anapproximately vertical main column, a plurality of approximatelyhorizontal plates spaced from each other in the column and adapted toretain a film of condensate on the top and bottom surfaces thereof, theplates covering only a portion of the cross sectional area of the columnand being so arranged in the column that the particular cross sectionalarea not covered by one plate is covered by the plates below and aboveit, means for collecting condensate from each plate and means forconveying the collected condensate in a protected path to the nextlowest plate.

. 6. A vacuum fractionating column of the character described andcomprising a plurality of approximately super-imposed plates, alternateplates being staggered in relation to one another so as to oifer slightresistance to the flow of vapors, means for allowing condensate to passin the form of a film over the top and bottom surface of each platesubstantially in the same direction of flow as the vapors, and means forconveying condensate from each of the plates to the next lowest plate,while protecting it from the vapor stream.

'7. A vacuum fractionating column of the character described, whichcomprises in combination, a main column casing, a plurality ofapproximately superimposed plates which offer slight resistance to theflow of vapors which are adapted to retain a thin film of condensate onthe top and bottom surface thereof and which are so disposed in thecolumn that the vapors and condensate travel in the same direction whenin contact with the top and bottom surfaces thereof and means forconveying condensate from each of the plates to the next lowest plate,while protecting it from the vapor stream.

8. A vacuum fractionating column comprising in combination anapproximately vertical cylindrical casing, a plurality of semi-circularplates having perforations about the circular edge thereof disposed atintervals upon the internal walls of the casing and in an approximatelyhorizontal position, each alternate plate being disposed upon theopposite wall of the casing, collecting gutters located under thestraight edge of each plate and conduits connecting each gutter to thetop straight edge of the next lowest plate.

9. A vacuum fractionating column comprising in combination, anapproximately vertical column casing, a series of plates, having smallperforations about their periphery and a large central opening, disposedin a horizontal position and at spaced intervals within the main casing,collecting gutters at the edges of the central openings of each plateand so located as to collect liquid flowing along the bottom surfaces ofthe plates, a second series of plates arranged .in alignment with andcorresponding in diameter to the central opening in the first series ofplates, and which are disposed between each pair of the first series ofplates, collecting gutters at the edges of the second series of platesand so located as to collect liquid flowing along the bottom surfacesthereof, a plurality of conduits connecting KENNETH C. D. HICKIWAN.

